Tantalum sputtering target and method for producing same

ABSTRACT

A tantalum sputtering target, wherein, on a sputtering surface of the tantalum sputtering target, an average crystal grain size is 50 μm or more and 150 μm or less, and a variation in a crystal grain size is 30 μm or less. A tantalum sputtering target, wherein, on a sputtering surface of the tantalum sputtering target, an orientation rate of a (200) plane exceeds 70%, an orientation rate of a (222) plane is 30% or less, an average crystal grain size is 50 μm or more and 150 μm or less, and a variation in a crystal grain size is 30 μm or less. By controlling the crystal grain size of the target, or the crystal grain size and the crystal orientation of the target, effects are yielded in that the discharge voltage of the tantalum sputtering target can be reduced so that plasma can be more easily generated, and the voltage drift during deposition can be suppressed.

BACKGROUND

The present invention relates to a tantalum sputtering target and amethod for producing such a tantalum sputtering target. In particular,the present invention relates to a tantalum sputtering target that isused for forming a Ta film or a TaN film as a diffusion barrier layer ofa copper wiring in Large-Scale Integration (LSI), and to a method forproducing such a tantalum sputtering target.

Conventionally, aluminum was used as the wiring material ofsemiconductor devices, but pursuant to the miniaturization and higherintegration of the devices, the problem of wiring delay became an issue,and copper having smaller electrical resistance than aluminum is nowbeing used. While copper is extremely effective as a wiring material,since copper itself is an active metal, there is a problem in thatcopper diffuses and contaminates the interlayer insulating film, and itis necessary to form a diffusion barrier layer made from a Ta film or aTaN film between the copper wiring and the interlayer insulating film.

Generally speaking, a Ta film or a TaN film is deposited by sputtering atantalum target. As factors that affect the performance of a tantalumtarget during sputtering, it is known that the various impurities andgas components contained in the target, and the plane orientation andcrystal grain size of the crystals affect the deposition rate, filmthickness uniformity, generation of particles, and the like.

For example, Patent Document 1 describes improving the uniformity of thefilm by forming a crystal structure in which the (222) orientation ispreferential from the position of 30% of the target thickness toward thecentral plane of the target.

Moreover, Patent Document 2 describes increasing the deposition rate andimproving the uniformity of the film by causing the crystal orientationof the tantalum target to be random (no alignment to a specific crystalorientation).

Moreover, Patent Document 3 describes improving the deposition rate byselectively increasing the plane orientations of (110), (200), (211),which have a high atomic density, on the sputtering surface, andimproving the uniformity by suppressing the variation in the planeorientation.

In addition, Patent Document 4 describes improving the film thicknessuniformity by causing the variation in the intensity ratio of the (110)plane obtained based on X-ray diffraction, depending on the location ofthe sputtering surface, to be within 20%.

Moreover, Patent Document 5 describes that a round metal target havingan extremely strong crystallographic texture such as (111) or (100) canbe prepared by combining swaging, extrusion, rotary forging, andnon-lubrication upset forging with clock rolling.

In addition, Patent Document 6 describes a method of producing atantalum sputtering target by subjecting a tantalum ingot to forging,annealing and rolling, and, after processing the tantalum ingot into itsfinal composition, performing annealing thereto at a temperature of 1173K or less to obtain a tantalum sputtering target having anon-recrystallized structure of 20% or less, or 90% or less.

Moreover, Patent Document 7 discloses a technique of stabilizing thesputtering characteristics by causing the relative intensity of the peakof the sputtering surface of the target to be (110)>(211)>(200) throughforging, cold rolling and other processes, and heat treatment.

In addition, Patent Document 8 describes forging a tantalum ingot,performing heat treatment two or more times during the foregoing forgingprocess, additionally performing cold rolling, and performingrecrystallization heat treatment.

Nevertheless, none of the foregoing Patent Documents describe theconcept of reducing the discharge voltage of the tantalum sputteringtarget so that plasma can be more easily generated and suppressing thevoltage drift during deposition by controlling the crystal grain size,or the crystal grain size and the crystal orientation, on the sputteringsurface of the target.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Patent Application Publication No.    2004-107758-   Patent Document 2: International Publication No. 2005/045090-   Patent Document 3: Japanese Patent Application Publication No.    H11-80942-   Patent Document 4: Japanese Patent Application Publication No.    2002-363736-   Patent Document 5: Japanese Translation of PCT International    Application Publication No. 2008-532765-   Patent Document 6: Japanese Patent No. 4754617-   Patent Document 7: International Publication No. 2011/061897-   Patent Document 8: Japanese Patent No. 4714123

DISCLOSURE OF THE INVENTION

An object of this invention is to reduce the discharge voltage of thetantalum sputtering target so that plasma can be more easily generated,and suppress the voltage drift curing deposition by controlling thecrystal grain size, or the crystal grain size and the crystalorientation, on the sputtering surface of the target.

In particular, an object of this invention is to provide a tantalumsputtering target that is effective in forming a diffusion barrier layermade from a Ta film or a TaN film capable of effectively preventingcontamination around the wiring caused by the diffusion of active Cu.

In order to resolve the foregoing problems, the present inventionprovides the following invention:

-   -   1) A tantalum sputtering target, wherein, on a sputtering        surface of the tantalum sputtering target, an average crystal        grain size is 50 μm or more and 150 μm or less, and a variation        in a crystal grain size is 30 μm or less.    -   2) A tantalum sputtering target, wherein, on a sputtering        surface of the tantalum sputtering target, an orientation rate        of a (200) plane exceeds 70%, an orientation rate of a (222)        plane is 30% or less, an average crystal grain size is 50 μm or        more and 150 μm or less, and a variation in a crystal grain size        is 30 μm or less.    -   3) A tantalum sputtering target, wherein, on a sputtering        surface of the tantalum sputtering target, an orientation rate        of a (200) plane is 80% or more, an orientation rate of a (222)        plane is 20% or less, an average crystal grain size is 50 μm or        more and 150 μm or less, and a variation in a crystal grain size        is 30 μm or less.    -   4) A thin film for a diffusion barrier layer formed using the        sputtering target according to any one of 1) to 3) above.    -   5) A semiconductor device that uses the thin film for a        diffusion barrier layer according to 4) above.

The present invention additionally provides:

-   -   6) A method of producing a tantalum sputtering target, wherein a        molten tantalum ingot is subject to forging and        recrystallization annealing, and thereafter subject to rolling        and heat treatment to form a crystal structure having, on a        sputtering surface of the target, an average crystal grain size        of 50 μm or more and 150 μm or less, and a variation in a        crystal grain size of 30 μm or less.    -   7) A method of producing a tantalum sputtering target, wherein a        molten tantalum ingot is subject to forging and        recrystallization annealing, and thereafter subject to rolling        and heat treatment to form a crystal structure having, on a        sputtering surface of the target, an orientation rate of a (200)        plane that exceeds 70%, an orientation rate of a (222) plane        that is 30% or less, an average crystal grain size of 50 μm or        more and 150 μm or less, and a variation in a crystal grain size        of 30 μm or less.    -   8) A method of producing a tantalum sputtering target, wherein a        molten tantalum ingot is subject to forging and        recrystallization annealing, and thereafter subject to rolling        and heat treatment to form a crystal structure having, on a        sputtering surface of the target, an orientation rate of a (200)        plane that is 80% or more, an orientation rate of a (222) plane        that is 20% or less, an average crystal grain size of 50 μm or        more and 150 μm or less, and a variation in a crystal grain size        of 30 μm or less.    -   9) The method of producing a tantalum sputtering target        according to anyone of 6) to 8) above, wherein cold rolling is        performed using a rolling mill roll having a rolling mill roll        diameter of 500 mm or less at a rolling speed of 10 m/min or        more and a reduction exceeding 80%.    -   10) The method of producing a tantalum sputtering target        according to anyone of 6) to 9) above, wherein heat treatment is        performed at a temperature of 900° C. to 1400° C.    -   11) The method of producing a tantalum sputtering target        according to anyone of 6) to 10) above, wherein, after rolling        and heat treatment are performed, surface finishing is performed        via machining or polishing.

The tantalum sputtering target of the present invention yields superioreffects of reducing the discharge voltage of the tantalum sputteringtarget so that plasma can be more easily generated and suppressing thevoltage drift during deposition by controlling the crystal grain size,or the crystal grain size and the crystal orientation, on the sputteringsurface of the target. The tantalum sputtering target of the presentinvention is particularly effective in forming a diffusion barrier layermade from a Ta film or a TaN film capable of effectively preventingcontamination around the wiring caused by the diffusion of active Cu.

DETAILED DESCRIPTION

One characteristic of the tantalum sputtering target of the presentinvention is that the average crystal grain size on the sputteringsurface thereof is 50 μm or more and 150 μm or less, and the variationin the crystal grain size is 30 μm or less. The average crystal grainsize affects the tantalum sputtering target discharge voltage. In otherwords, since the discharge voltage can be reduced to stabilize theplasma, and the voltage drift during deposition can be suppressed byadjusting the average crystal grain size to be within the foregoingrange, it is possible to suppress the generation of dischargeabnormalities during the sputtering process described above. Inparticular, it is possible to cause the discharge voltage to be 620 V orless and cause the variation in the discharge voltage to be 20 V orless, and the discharge abnormality occurrence rate can thereby bereduced. When the average crystal grain size is outside the range of 50μm or more and 150 μm or less, in either case the effect of stabilizingthe plasma and suppressing the voltage drift during deposition tends todeteriorate.

In addition to the adjustment of the foregoing average crystal grainsize, by increasing the orientation rate of the (200) plane and reducingthe orientation rate of the (222) plane, the characteristic ofsuppressing the generation of discharge abnormalities during sputteringcan be further improved.

Since the crystal structure of tantalum is a body-centered cubic latticestructure (abbreviated as BCC), the (222) plane has a shorterinteratomic distance than the (200) plane, and the (222) plane is in astate where the atoms are more densely packed than the (200) plane.Thus, during sputtering, it is considered that the (222) planedischarges more tantalum atoms than the (200) plane, which in turncauses the sputter rate (deposition rate) to increase.

With the tantalum sputtering target of the present invention, on thesputtering surface of the tantalum sputtering target, the averagecrystal grain size is 50 μm or more and 150 μm or less, and thevariation in the crystal grain size is 30 μm or less, and furthermorethe orientation rate of the (200) plane exceeds 70%, and the orientationrate of the (222) plane is 30% or less. Preferably, the orientation rateof the (200) plane is 80% or more, and the orientation rate of the (222)plane is 20% or less.

By increasing the orientation rate of the (200) plane and reducing theorientation rate of the (222) plane on the sputtering surface asdescribed above, under normal conditions the sputter rate (depositionrate) would deteriorate. Nevertheless, when there is no need toexcessively increase the deposition rate, since the tantalum sputteringtarget discharge voltage can be lowered, there are advantages in thatplasma can be more easily generated, and plasma can be stabilized.

Normally, when depositing a tantalum film via sputtering, the voltageand current are adjusted so that the discharge can be maintained at thesupplied power that was set. Nevertheless, there are cases where thecurrent decreases due to some reason or other and the voltage increasesin order to maintain the power at a constant value, and this kind ofstate is generally referred to as a discharge abnormality.

The present invention is able to suppress the generation of dischargeabnormalities during sputtering as described above by controlling thecrystal grain size, or the crystal grain size and the crystalorientation, on the sputtering surface of the tantalum sputteringtarget, and additionally increasing the orientation rate of the (200)plane and decreasing the orientation rate of the (222) plane as needed,and thereby reduce the discharge voltage of the sputtering target andstabilize the plasma. In particular, it is possible to cause thedischarge voltage to be 620 V or less and cause the variation in thedischarge voltage to be 20 V or less, and the discharge abnormalityoccurrence rate can thereby be reduced.

In the present invention, the term “orientation rate” refers to theintensity ratio of a specific plane orientation when the measuredintensity of the respective diffraction peaks of (110), (200), (211),(310), (222), (321) obtained with the X-ray diffraction method arestandardized, and the sum of the intensities of the respective planeorientations is 100. Note that JCPDS (Joint Committee for PowderDiffraction Standard) was used for the standardization.

For example, the orientation rate (%) of the (200) plane will be{(measured intensity of (200)/JCPDS intensity of (200))/Σ(measuredintensity of respective planes/JCPDS intensity of respectiveplanes)}×100.

The tantalum sputtering target of the present invention may be used forforming a diffusion barrier layer made from a Ta film or a TaN film in acopper wiring. Even in cases of introducing nitrogen into the sputteringatmosphere to deposit a TaN film, the sputtering target of the presentinvention yields superior effects of reducing the discharge voltage ofthe tantalum sputtering target so that plasma can be more easilygenerated and improving the stability of plasma by controlling thecrystal grain size, or the crystal grain size and the crystalorientation, on the sputtering surface of the target, and additionallyincreasing the orientation rate of the (200) plane and reducing theorientation rate of the (222) plane. Thus, the present invention canimprove the production yield in the formation of copper wiringscomprising a diffusion barrier layer made from a Ta film or a TaN film,and in the manufacture of semiconductor devices comprising such as acopper wiring.

The tantalum sputtering target of the present invention is producedaccording to the following processes. To illustrate an example,foremost, high purity tantalum having a purity of 4N (99.99%) or higheris normally used as the tantalum raw material. The tantalum raw materialis melted via electron beam melting or the like and subsequently cast toprepare an ingot or a billet. Subsequently, the ingot or the billet issubject to forging, and recrystallization annealing. Specifically, forexample, the ingot or the billet is subject to extend forging—annealingat a temperature of 1100 to 1400° C.—cold forging (primaryforging)—annealing at a temperature of recrystallization temperature to1400° C.—cold forging (secondary forging)—annealing at a temperature ofrecrystallization temperature to 1400° C.

Cold rolling is subsequently performed. The orientation rate of thetantalum sputtering target of the present invention can be controlled byadjusting the cold rolling conditions. Specifically, a rolling mill rollwith a small roll diameter should be used, and preferably the rolldiameter is 500 mm or less. Moreover, the rolling speed should be asfast as possible, and preferably 10 m/min or more. In addition, whenrolling is only performed once, the reduction is preferably high and inexcess of 80%, and when rolling is to be repeated two or more times, thereduction needs to be 60% or higher so that the ultimate thickness ofthe target becomes the same as the case of only performing rolling once.Desirably, the total amount of reduction exceeds 80%.

Heat treatment is subsequently performed. The orientation rate of thetantalum sputtering target of the present invention can be controlled byadjusting the conditions of the heat treatment performed after coldrolling in addition to adjusting the cold rolling conditions.Specifically, the heat treatment temperature should be high, andpreferably 900 to 1400° C. While this will also depend on the amount ofstrain that is introduced from the rolling process, heat treatment needsto be performed at a temperature of 900° C. or higher in order to obtaina recrystallized structure. Meanwhile, to perform heat treatment at atemperature that exceeds 1400° C. is undesirable in terms of cost.Subsequently, the surface of the target is subject to surface finishingvia machining or polishing in order to obtain the final product.

The tantalum sputtering target is produced based on the foregoingproduction processes, but what is particularly important in the presentinvention is to control the crystal grain size, or the crystal grainsize and the crystal orientation, on the sputtering surface of thetarget, and to additionally increase the orientation rate of the (200)plane and decrease the orientation rate of the (222) plane in thecrystal orientation on the sputtering surface of the target as needed.

The rolling process is mainly responsible for controlling the crystalgrain size and the crystal orientation. In the rolling process, it ispossible to change the amount and distribution of strain that isintroduced from the rolling process by controlling parameters such asthe diameter of the rolling mill roll, rolling speed, and reduction, andthe orientation rate of the (200) plane and the orientation rate of the(222) plane can thereby be controlled.

In order to effectively adjust the crystal grain size or the orientationrate, the condition setting needs to be repeated a certain number oftimes, but once the crystal grain size and the orientation rate of the(200) plane and the orientation rate of the (222) plane are adjusted,targets having constant characteristics i.e., characteristics of aconstant level can be produced by setting the manufacturing conditions.

Normally, upon producing a target, it is effective to use a rolling millroll having a rolling mill roll diameter of 500 mm or less, set therolling speed to 10 m/min or more, set the reduction of 1 pass to 8 to12%, and set the number of passes to 15 to 25 passes. Nevertheless, theproduction process is not necessarily limited to the foregoingproduction process so as long as the production process can achieve thecrystal orientation of the present invention. In the series ofprocesses, a condition setting of destroying the cast structure viaforging and rolling and sufficiently performing recrystallization iseffective. While there is no particular limitation to the roll material(ceramic roll, metal roll) used in the cold rolling process, it is moreeffective to use a rigid roll.

In addition, after subjecting the molten tantalum ingot or billet toforging, rolling and other processes, the product is desirably subjectto recrystallization annealing to obtain a fine and uniform structure.

EXAMPLES

The present invention is now explained based on the Examples. Thefollowing Examples are provided to facilitate the understanding of thepresent invention, and the present invention is not in any way limitedby these Examples. In other words, modifications and other examplesbased on the technical concept of the present invention are obviouslycovered by the present invention.

A tantalum raw material having a purity of 99.995% was subject toelectron beam melting and casting to obtain an ingot having a diameterof 195 mmφ. Subsequently, the ingot was subject to extend forging atroom temperature to obtain a diameter of 150 mmφ, and the product wassubject to recrystallization annealing at a temperature of 1100 to 1400°C. The product was once again subject to forging at room temperature toobtain a thickness of 100 mm and a diameter of 150 mmφ (primaryforging), and the product was subject to recrystallization annealing ata temperature of recrystallization temperature to 1400° C. In addition,the product was subject to forging at room temperature to obtain athickness of 70 to 100 mm and a diameter of 150 to 185 mmφ (secondaryforging), and the product was subject to recrystallization annealing ata temperature of recrystallization temperature to 1400° C. to obtain atarget material.

Example 1

In Example 1, the obtained target material was subject to cold rollingusing a rolling mill roll having a rolling mill roll diameter of 400 mmat a rolling speed of 10 m/min, 20 passes at a reduction of 10%, and atotal reduction of 88% to obtain a thickness of 14 mm and a diameter of520 mmφ. The product was subject to heat treatment at a temperature of1400° C. Subsequently, the surface of the product was machined andpolished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 82.6% and the orientation rate of the (222) plane is13.4%, an average crystal grain size of 127.1 μm, and a variation in thecrystal grain size is 28.0 μm.

Note that the crystal grain size was measured using analySIS FIVE (Softimaging System) and analyzing the crystal structure photograph taken ina visual field of 1500 μm×1200 μm with an electronic microscope.Moreover, as the variation in the crystal grain size, the crystal grainsize at 5 locations on the target plane [center+4 locations (2 locationsat the outer periphery in the perpendicular direction, and points thatare halfway between the center and the 2 locations at the outerperiphery)] was measured, and the average value and the standarddeviation were calculated to obtain (variation (%)=standarddeviation/average value×100). Measurement was performed in the samemanner in the following Examples and Comparative Examples.

As a result of sputtering this sputtering target, the discharge voltagewas 615.3 V, the discharge voltage variation was 14.5 V, and thedischarge abnormality occurrence rate was favorable at 5.3%. The resultsare shown in Table 1.

Normally, upon calculating the discharge abnormality occurrence rate,the number of times that the voltage reached 1000 V as the upper limitof the power source is divided by the total number of discharges, and inthis Example also, the discharge abnormality occurrence rate wascalculated under the same conditions. The tantalum film was depositedunder the following conditions (same in the ensuing Examples andComparative Examples).

<Deposition Conditions>

Power source: DC system

Electrical power: 15 kW

Ultimate vacuum: 5×10⁻⁸ Torr

Atmosphere gas composition: Ar

Sputter gas pressure: 5×10⁻³ Torr

Sputtering time: 15 seconds

Example 2

In Example 2, the obtained target material was subject to cold rollingusing a rolling mill roll having a rolling mill roll diameter of 400 mmat a rolling speed of 15 m/min, 25 passes at a reduction of 9%, and atotal reduction of 90% to obtain a thickness of 14 mm and a diameter of520 mmφ. The product was subject to heat treatment at a temperature of800° C. Subsequently, the surface of the product was machined andpolished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 77.6% and the orientation rate of the (222) plane is7.0%, an average crystal grain size of 66.3 μm, and a variation in thecrystal grain size is 19.0 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 611.4 V, the discharge voltage variation was 12.6 V, and thedischarge abnormality occurrence rate was favorable at 3.1%. The resultsare shown in Table 1.

Example 3

In Example 3, the obtained target material was subject to cold rollingusing a rolling mill roll having a rolling mill roll diameter of 400 mmat a rolling speed of 20 m/min, 23 passes at a reduction of 8%, and atotal reduction of 85% to obtain a thickness of 14 mm and a diameter of520 mmφ. The product was subject to heat treatment at a temperature of1000° C. Subsequently, the surface of the product was machined andpolished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 74.1% and the orientation rate of the (222) plane is11.9%, an average crystal grain size of 80.4 μm, and a variation in thecrystal grain size is 25.6 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 612.3 V, the discharge voltage variation was 9.8 V, and thedischarge abnormality occurrence rate was favorable at 6.4%. The resultsare shown in Table 1.

Example 4

In Example 4, the obtained target material was subject to cold rollingusing a rolling mill roll having a rolling mill roll diameter of 500 mmat a rolling speed of 15 m/min, 18 passes at a reduction of 12%, and atotal reduction of 90% to obtain a thickness of 14 mm and a diameter of520 mmφ. The product was subject to heat treatment at a temperature of900° C. Subsequently, the surface of the product was machined andpolished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 71.7% and the orientation rate of the (222) plane is14.9%, an average crystal grain size of 51.9 μm, and a variation in thecrystal grain size is 16.4 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 611.8 V, the discharge voltage variation was 17.7 V, and thedischarge abnormality occurrence rate was favorable at 4.5%. The resultsare shown in Table 1.

Example 5

In Example 5, the obtained target material was subject to cold rollingusing a rolling mill roll having a rolling mill roll diameter of 500 mmat a rolling speed of 20 m/min, 15 passes at a reduction of 12%, and atotal reduction of 85% to obtain a thickness of 14 mm and a diameter of520 mmφ. The product was subject to heat treatment at a temperature of1200° C. Subsequently, the surface of the product was machined andpolished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 70.3% and the orientation rate of the (222) plane is16.1%, an average crystal grain size of 98.1 μm, and a variation in thecrystal grain size is 24.8 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 612.6 V, the discharge voltage variation was 7.6 V, and thedischarge abnormality occurrence rate was favorable at 9.6%. The resultsare shown in Table 1.

Comparative Example 1

In Comparative Example 1, the obtained target material was subject tocold rolling using a rolling mill roll having a rolling mill rolldiameter of 650 mm at a rolling speed of 15 m/min, 10 passes at areduction of 15%, and a total reduction of 80% to obtain a thickness of14 mm and a diameter of 520 mmφ. The product was subject to heattreatment at a temperature of 800° C. Subsequently, the surface of theproduct was machined and polished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 43.6% and the orientation rate of the (222) plane is39.1%, an average crystal grain size of 74.4 μm, and a variation in thecrystal grain size is 48.2 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 622.5 V, the discharge voltage variation was 17.0 V, and thedischarge abnormality occurrence rate was inferior at 16.6%. The resultsare shown in Table 1.

Comparative Example 2

In Comparative Example 2, the obtained target material was subject tocold rolling using a rolling mill roll having a rolling mill rolldiameter of 500 mm at a rolling speed of 10 m/min, 11 passes at areduction of 13%, and a total reduction of 78% to obtain a thickness of14 mm and a diameter of 520 mmφ. The product was subject to heattreatment at a temperature of 800° C. Subsequently, the surface of theproduct was machined and polished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 64.8% and the orientation rate of the (222) plane is15.1%, an average crystal grain size of 64.2 μm, and a variation in thecrystal grain size is 49.6 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 627.0 V, the discharge voltage variation was 18.0 V, and thedischarge abnormality occurrence rate was inferior at 20.5%. The resultsare shown in Table 1.

Comparative Example 3

In Comparative Example 3, the obtained target material was subject tocold rolling using a rolling mill roll having a rolling mill rolldiameter of 500 mm at a rolling speed of 20 m/min, 32 passes at areduction of 7%, and a total reduction of 90% to obtain a thickness of14 mm and a diameter of 520 mmφ. The product was subject to heattreatment at a temperature of 800° C. Subsequently, the surface of theproduct was machined and polished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 71.2% and the orientation rate of the (222) plane is18.3%, an average crystal grain size of 39.8 μm, and a variation in thecrystal grain size is 10.9 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 610.4 V, the discharge voltage variation was 24.2 V, and thedischarge abnormality occurrence rate was inferior at 26.2%. The resultsare shown in Table 1.

Comparative Example 4

In Comparative Example 4, the obtained target material was subject tocold rolling using a rolling mill roll having a rolling mill rolldiameter of 500 mm at a rolling speed of 20 m/min, 9 passes at areduction of 20%, and a total reduction of 86% to obtain a thickness of14 mm and a diameter of 520 mmφ. The product was subject to heattreatment at a temperature of 1000° C. Subsequently, the surface of theproduct was machined and polished to obtain a target.

Based on the foregoing processes, it was possible to obtain a tantalumsputtering target having a crystal structure in which the orientation ofthe (200) plane is 71.6% and the orientation rate of the (222) plane is12.1%, an average crystal grain size of 142.0 μm, and a variation in thecrystal grain size is 46.8 μm.

As a result of sputtering this sputtering target, the discharge voltagewas 603.4 V, the discharge voltage variation was 28.4 V, and thedischarge abnormality occurrence rate was inferior at 18.3%. The resultsare shown in Table 1.

As shown in the foregoing Examples and Comparative Examples, thosewithin the range of the conditions of the present invention yieldeffects of reducing the discharge voltage of the tantalum sputteringtarget so that plasma can be more easily generated and improving thestability of the plasma. In other words, in comparison to theComparative Examples, superior effects are yielded in that the dischargevoltage can be reduced, variation in the discharge voltage can besuppressed, and the discharge abnormality occurrence rate can also bereduced.

TABLE 1 Discharge (200) (222) Discharge abnormality orientationorientation Average grain Grain size Discharge voltage occurrence rate(%) rate (%) size (um) variation (um) voltage (V) Maximum (V) Minimum(V) variation (V) rate (%) Example 1 82.6 13.4 127.1 28 615.3 615.1600.6 14.5 5.3 Example 2 77.6 7 66.3 19 611.4 617.5 604.9 12.6 3.1Example 3 74.1 11.9 80.4 25.6 612.3 617.2 607.4 9.8 6.4 Example 4 71.714.9 51.9 16.4 611.8 619.3 601.6 17.7 4.5 Example 5 70.3 16.1 98.1 24.8612.6 616.4 608.8 7.6 9.6 Comparative 43.6 39.1 74.4 48.2 622.5 631 61417 16.6 Example 1 Comparative 64.8 15.1 64.2 49.6 627 636 618 18 20.5Example 2 Comparative 71.2 18.3 39.8 10.9 610.4 617.8 593.6 24.2 26.2Example 3 Comparative 71.6 12.1 142 46.8 603.4 620.7 592.3 28.4 18.3Example 4

The present invention provides a tantalum sputtering target, and bycontrolling the crystal grain size, or the crystal grain size and thecrystal orientation, on the sputtering surface of the target, effectsare yielded in that the discharge voltage of the tantalum sputteringtarget can be reduced so that plasma can be more easily generated, andthe stability of the plasma can be improved. The tantalum sputteringtarget of the present invention is particularly effective in forming adiffusion barrier layer made from a Ta film or a TaN film capable ofeffectively preventing contamination around the wiring caused by thediffusion of active Cu.

The invention claimed is:
 1. A tantalum sputtering target, wherein, on asputtering surface of the tantalum sputtering target, an orientationrate of a (200) plane is 70.3% or more and 82.6% or less, an orientationrate of a (222) plane is 7.0% or more and 16.1% or less, a sum total oforientation ratios of a (110) plane, a (211) plane, a (310) plane, and a(321) plane is 4% or more and 15.4% or less, an average crystal grainsize is 50 μm or more and 150 μm or less, and a variation in a crystalgrain size is 30 μm or less, and wherein the orientation rate is anintensity ratio of a specific plane orientation in which a measuredintensity of the respective diffraction peaks of (110), (200), (211),(310), (222), (321) obtained with X-ray diffraction are standardized anda sum of the intensities of the respective plane orientations is
 100. 2.The tantalum sputtering target according to claim 1, wherein JointCommittee for Powder Diffraction Standard (JCPDS) is used forstandardization such that the orientation rate of the (200) plane isexpressed as ((measured intensity of (200)/JCPDS intensity of(200))/Σ(measured intensity of respective planes/JCPDS intensity ofrespective planes))×100, and the orientation rate of the (222) plane isexpressed as ((measured intensity of (222)/JCPDS intensity of(222))/Σ(measured intensity of respective planes/JCPDS intensity ofrespective planes))×100.
 3. A method of producing a tantalum sputteringtarget, wherein a molten tantalum ingot is subject to forging andrecrystallization annealing, and thereafter subject to rolling and heattreatment to form a crystal structure having, on a sputtering surface ofthe target, an orientation rate of a (200) plane that is 70.3% or moreand 82.6% or less, an orientation rate of a (222) plane that is 7.0% ormore and 16.1% or less, a sum total of orientation ratios of a (110)plane, a (211) plane, a (310) plane, and a (321) plane that is 4% ormore and 15.4% or less, an average crystal grain size of 50 μm or moreand 150 μm or less, and a variation in a crystal grain size of 30 μm orless, and wherein the orientation rate is an intensity ratio of aspecific plane orientation in which a measured intensity of therespective diffraction peaks of (110), (200), (211), (310), (222), (321)obtained with X-ray diffraction are standardized and a sum of theintensities of the respective plane orientations is
 100. 4. The methodof producing a tantalum sputtering target according to claim 3, whereinthe rolling is cold rolling performed using a rolling mill roll having arolling mill roll diameter of 500 mm or less at a rolling speed of 10m/min or more and a reduction exceeding 80%.
 5. The method of producinga tantalum sputtering target according to claim 4, wherein the heattreatment is performed at a temperature of 900° C. to 1400° C.
 6. Themethod of producing a tantalum sputtering target according to claim 5,wherein, after the rolling and heat treatment are performed, surfacefinishing is performed via machining or polishing.
 7. The methodaccording to claim 3, wherein the heat treatment is performed at atemperature of 900° C. to 1400° C.
 8. The method according to claim 3,wherein, after the rolling and heat treatment are performed, surfacefinishing is performed via machining or polishing.
 9. The methodaccording to claim 3, wherein Joint Committee for Powder DiffractionStandard (JCPDS) is used for standardization such that the orientationrate of the (200) plane is expressed as ((measured intensity of(200)/JCPDS intensity of (200))/Σ(measured intensity of respectiveplanes/JCPDS intensity of respective planes))×100, and the orientationrate of the (222) plane is expressed as ((measured intensity of(222)/JCPDS intensity of (222))/Σ(measured intensity of respectiveplanes/JCPDS intensity of respective planes))×100.